Surface plasmon indicates collective charge density oscillation generated on a surface of a metal thin film, and a surface plasmon wave generated by the surface plasmon is a surface electromagnetic wave moving along a boundary surface between a metal and a dielectric. This will be described below in more detail. A great number of free electrons are present in the metal, which is a conductor. Since the free electrons are not bound to metal atoms, they may easily respond to an external specific stimulus. A phenomenon that electrons in the material as described above simultaneously oscillate is called plasmon. Particularly, when a size of a surface structure of the metal is a nano level, a surface plasmon resonance phenomenon that the metal has a unique optical property due to behavior of these free electrons appears.
The surface plasmon resonance phenomenon indicates a phenomenon that the free electrons of a surface of the metal collectively oscillate due to resonance with an electromagnetic field of specific energy of light when the light is incident between surfaces of metal nano particles, which are conductors, and a dielectric such as air, water, or the like. That is, in the metal nano particles, an electric field of light in a visible ray to near-infrared ray band and a plasmon are paired with each other, such that light absorption is generated, thereby representing a clear color (in this case, another similar particle generated by coupling the plasmon and a photon to each other is called a surface plasmon polariton). This phenomenon is called a surface plasmon resonance phenomenon, and has an effect that an electromagnetic field is significantly amplified in local regions, which are peripheral portions of metal nano structures. This local surface plasmon resonance phenomenon is induced by conductive nano particles or metal nano structures having a size smaller than a wavelength of incident light, and a frequency of the surface plasmon resonance is changed by sizes or forms of the metal nano particles, a solvent in which the metal nano particles are dispersed, or the like.
One of the typical technologies using the surface plasmon resonance phenomenon as described above is a surface-enhanced Raman spectroscopy (SERS). The surface-enhanced Raman spectroscopy (SERS) is to perform measurement using a phenomenon that Raman-scattering signals, which are unique spectra appearing when light passes through a material, are amplified billions of times on surfaces on which nano structures are formed, by the local surface plasmon resonance as described above. In more detail, when a target material to be detected is coated on a substrate on which the nano structures are formed and light is incident to the substrate, the Raman-scattering signals are generated and amplified by the target material to be detected, and are detected, thereby making it possible to decide the corresponding material. The surface-enhanced Raman spectroscopy as described above has been widely used in various fields such as pharmaceutical field, material science field, drug detection field, and bio-molecule detection field, and the like.
Meanwhile, in the case of a general semiconductor based electronic device circuit, which has a size of tens of nanometers or less, a degree of integration of the circuit is high, while it is difficult for a frequency speed of a signal to exceed 10 GHz. Therefore, research into an optical device as an alternative to the electronic device has been actively conducted. The optical device has a large advantage that a high speed of 100 GHz may be obtained, but also has a diffraction limitation of light, such that it is difficult to reduce a size of a basic device to about hundreds of nanometers or less. As a result, it is difficult to increase a degree of integration of a circuit. That is, an existing dielectric based optical device may not confine light in a region smaller than a wavelength, such that it may not be manufactured at a size as small as the electronic device.
However, as described above, at the time of the surface plasmon resonance, an effect that the electromagnetic field is significantly amplified in the local regions, which are the peripheral portions of the metal nano particles, appears, which means that light energy is converted on a surface plasmon to thereby be accumulated on surfaces of the metal nano particles. This also means that light may be controlled in a region smaller than the diffraction limitation of the light. Therefore, research into an optical device using the plasmon resonance has been variously conducted actively.
An example of a technology developed depending on this research includes Korean Patent Laid-Open Publication No. 10-2015-0138890 (entitled “Method of Preparing Surface Plasmon Resonance-based Light Emitting Diode Using Insulator Film and published on Dec. 11, 2015) (hereinafter, referred to as Related Art Document 1), Korean Patent No. 1559194 (entitled “Surface Plasmon Resonance Optical Materials Using Conductive Oxide Nanoparticles, Method for Fabricating the Same and Optical Devices Comprising the Same” and registered on Oct. 2, 2015) (hereinafter, referred to as Related Art Document 2), and the like. In Related Art Document 1, a light emitting diode (LED) device configured to include a first semiconductor layer, a second semiconductor layer, an active layer interposed between the first semiconductor layer and the second semiconductor layer, hole patterns repeatedly formed periodically in the second semiconductor layer, metal regions positioned in the hole patterns, insulator films formed between the hole patterns and the metal regions has been disclosed. The light emitting diode according to Related Art Document 1 is configured to improve light emitting efficiency by generating a plasmon resonance phenomenon between the active layer of the LED structure and the metal regions enclosed by protection films. In Related Art Document 2, an optical material configured to include a medium including a dielectric or a semiconductor and conductive oxide nano particles buried in the medium and interacting with light in a visible ray to ultraviolet ray region to generate surface plasmon resonance has been disclosed.
It may be appreciated from these Related Art Documents that an existing optical device using the surface plasmon resonance is not appropriate for being used to transfer signals and is limited to only a simple light emitting device. As described above, the optical device that is to be used as the alternate to the electronic device should be able to transfer the signals. That is, the optical device should have a light emitting structure, a light receiving structure, and a link structure between the light emitting structure and the light receiving structure. However, in the case of Related Art Documents, these functions may not be realized.
Therefore, a demand for a configuration of an optical device that may ultimately substitute for the electronic device or may be combined with the electronic device by having the light emitting structure, the light receiving structure, and the link structure between the light emitting structure and the light receiving structure has gradually increased.